[ticket/11995] Add unit test for reverting config.remove

PHPBB3-11995
[ticket/11995] Fix Revert of config.remove

PHPBB3-11995
[ticket/11995] Remove exceptions and split reverse into different tests

PHPBB3-11995
Merge pull request #1847 from nickvergessen/ticket/11995

Ticket/11995 Fix Revert of config.remove migration